This invention relates generally to endoluminal stents, grafts, and/or prostheses and, more specifically, to stents having multiple longitudinal sections of different stent architecture.
A stent is an elongated device used to support an intraluminal wall. In the case of a stenosis, a stent provides an unobstructed conduit for blood in the area of the stenosis. Such a stent may also have a prosthetic graft layer of fabric or covering lining the inside or outside thereof, such a covered stent being commonly referred to in the art as an intraluminal prosthesis, an endoluminal or endovascular graft (EVG), or a stent-graft.
A prosthesis may be used, for example, to treat a vascular aneurysm by removing the pressure on a weakened part of an artery so as to reduce the risk of rupture. Typically, a prosthesis is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called xe2x80x9cminimally invasive techniquesxe2x80x9d in which the prosthesis, restrained in a radially compressed configuration by a sheath or catheter, is delivered by a deployment system or xe2x80x9cintroducerxe2x80x9d to the site where it is required. The introducer may enter the body through the patient""s skin, or by a xe2x80x9ccut downxe2x80x9d technique in which the entry blood vessel is exposed by minor surgical means. When the introducer has been threaded into the body lumen to the prosthesis deployment location, the introducer is manipulated to cause the prosthesis to be ejected from the surrounding sheath or catheter in which it is restrained (or alternatively the surrounding sheath or catheter is retracted from the prosthesis), whereupon the prosthesis expands to a predetermined diameter at the deployment location, and the introducer is withdrawn. Stent expansion may be effected by spring elasticity, balloon expansion, or by the self-expansion of a thermally or stress-induced return of a memory material to a pre-conditioned expanded configuration.
Various types of stent architectures are known in the art, including many designs comprising a filament or number of filaments, such as a wire or wires, wound or braided into a particular configuration. Included among these wire stent configurations are braided stents, such as is described in U.S. Pat. No. 4,655,771 to Hans I. Wallsten and incorporated herein by reference, the ""771 Wallsten patent being only one example of many variations of braided stents known in the art and thus not intended as a limitation of the invention described herein later. Braided stents tend to be very flexible, having the ability to be placed in tortuous anatomy and still maintain patency. This flexibility of braided stents make them particularly well-suited for treating aneurysms in the aorta, where often the lumen of the vessel becomes contorted and irregular both before and after placement of the stent.
Braided stents also have several disadvantages, however. One such disadvantage is that the radial strength on the end of the braided stent is typically substantially less than the radial strength in the middle of the stent. Insufficient radial strength on the stent ends can result in an incomplete seal or migration of the device after implantation. Although flaring the ends or covering the stent with a graft can enhance the radial strength of the ends, the radial strength may still be insufficient. Also, when a braided stent is placed around a curve so that the end of the stent terminates within the curve, tapering of the stent end can result. This can also result in poor end sealing and migration. This phenomenon is particularly prevalent in stents greater than 16 mm in diameter. Although such tapering can be minimized by optimizing braid characteristics such as for example, wire count, wire diameter, and end flare, this tapering effect is still of significant concern.
A number of other stent designs are known in the art having greater radial strength but also having less flexibility than braided stents. Such stent designs can be combined with a braided stent design to produce a multi-segment stent having a flexible, braided stent member in the middle and less-flexible, higher-radial-strength stent members on the ends. Referring now to FIG. 18, one known way of combining such stents is merely to implant a braided stent 180 across a region to be repaired (not shown), and then to implant a higher-radial-strength stent 182 overlapping one or both ends 184 of the braided stent to more strongly anchor the braided stent to the lumen (not shown). Such a procedure, however, requires the implantation of multiple stents.
Referring now to FIGS. 1 and 2, it is also known, for example, to attach a braided stent member 2 to radially strong, rigid tubular stent end members 1 and 11. Braided stent member 2 comprises meshing wires 7 that criss-cross to form knots or overlaps 8. Wires 7 of braided stent member 2 are welded to flanges 6 of tubular stent end members 1 and 11 in pairs. This configuration is described in detail in U.S. Pat. No. 5,383,892 to Cardon et al. (hereinafter xe2x80x9cCardonxe2x80x9d).
In another configuration, described in detail in U.S. Pat. No. 5,817,126 to Imran, strands or ribbons of metal are attached to opposite ends comprising slotted metal stents. The strands or ribbons are then intertwined to form a braided middle section.
The configuration disclosed in Cardon and Imran, however, while being applicable for providing a braided stent joined to a slotted metal stent, does not address joining a flexible, filamentary braided stent to a more rigid, wound filamentary stent. Filamentary stents of various winding configurations are well-known in the art, having various degrees of flexibility or rigidity. Inasmuch as such wound filamentary stents do not have discrete flanges as shown in FIGS. 1 and 2 and described in Cardon or flat areas of slotted metal for joining ribbons or strands as described in Imran, a wound filamentary stent cannot be joined to a braided filamentary stent as described in Cardon or Imran. It may also be desirable to provide more continuity between the end and middle sections than is offered by the mere welding of the ends of the wires or ribbons of the braided section to flanges or other elements of the slotted metal ends, such welding points potentially forming weak spots in the overall stent construction. Additionally, it may be desired to provide stents with variable radial strength sections having diameters larger than can be readily provided by slotted metal stents. In particular, it is desirable to provide multi-section stents wherein the flexible middle section and the more rigid end sections all comprise filamentary stents.
According to an embodiment of the invention, a multi-section filamentary stent comprises a braided section, which is a cylindrical mesh of a first set of filaments, and at least one wound section, which is connected to the braided section and which comprises a second set of one or more filaments in a repeating configuration having at least one bent portion. For example, a braided center section may be connected between two wound end sections. The repeating configuration of the second set of filaments in the wound section may comprise: a zig-zag configuration, an overlapping zig-zag configuration, a helical configuration, a non-helical configuration, or a configuration having polygonal cells. The polygonal cells may comprise hexagonal cells or overlapping hexagonal cells. At least one continuous filament may be a member of both the first set of filaments in the braided section and the second set of filaments in the wound section, serving to connect the two sections. In one exemplary configuration, at least one continuous filament may extend from the wound section into the braided section as a redundant filament, a tracer filament, or a redundant tracer filament.
The braided section is preferably connected to the wound section by virtue of at least one of the filaments being a member of both sets of filaments. The sections may also be connected to one another by sutures or welding, by a common graft providing a connection between the braided section and the wound section, or by one or more filaments of the braided section looped around apices of the wound sections, or by at least one filament of the wound section looping around at least one overlap in the braided section. At least a portion of the wound section may overlap and interlock with a portion of the braided section.
According to another embodiment of the invention, a multi-section filamentary stent comprises a first section, having a first stent architecture comprising one or more filaments in a first geometric configuration, and a second section, having a second stent architecture comprising one or more filaments in a second geometric configuration. The first stent architecture has a first flexibility and a first radial strength, and the second stent architecture has a second flexibility less than the first flexibility and a second radial strength greater than the first radial strength. The first stent architecture comprises a braided stent architecture. At least one continuous filament extends into both the first and second sections. The stent may comprise a middle section having the first stent architecture positioned between a distal end section and a proximal end section, each end section having the second stent architecture. The distal end section and the proximal end section may be identical or different in length and/or architecture. In particular, where the distal end is adapted to be positioned in a lumen upstream of the proximal end section relative to intraluminal fluid flow, the length of the distal end may be greater or the architecture may have a greater radial strength than the proximal end.
According to still another aspect of the invention, the stent comprises a first section having a first, braided stent architecture with a first shortening ratio, and a second section having a second stent architecture with a second shortening ratio. The shortening ratio is the length of a section in its radially compressed configuration (typically longer) divided by its length in its radially expanded configuration (typically shorter). The first shortening ratio is greater than the second shortening ratio. The stent comprises at least one continuous filament contained in both the first and second sections.
The invention also comprises various forms of the stent, including a single stent adapted for individual delivery in a body lumen, two or more modular components adapted for joining together in situ in a non-branching lumen, and two or more modular components adapted for joining together in situ in a branching lumen.
A stent according to the present invention may also comprise a first section, having a first, braided stent architecture comprising one or more filaments in a first geometric configuration and having a first percentage of open area, and a second section, having a second stent architecture comprising one or more filaments in a second geometric configuration and having a second percentage of open area greater than the first percentage. The stent comprises at least one continuous filament contained in both the first and second sections. The first section of such a stent may be adapted for deployment in a first portion of a body lumen having no intersecting lumen connected thereto, whereas the second section is adapted for deployment in a second portion of the body lumen having one or more intersecting lumen connected thereto.
A stent according to the present invention may also comprise a first section having a first stent architecture comprising one or more filaments in a first geometric configuration, wherein the first stent architecture has a first radial strength and a known end effect comprising a reduction in radial strength along end lengths of the architecture. A second section of the stent, having a second stent architecture comprising one or more filaments in a second geometric configuration, has a radial strength substantially equal to the first radial strength or at least greater than the radial strength imparted by the end effect, and comprises an end section connected to the first section to counteract the end effect of the first stent architecture.
The present invention further comprises a method of treating a body lumen by implantation of any of the stent structures described herein.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention.